Flue gas, which may derive from a power station, is often introduced at the lower part of the scrubbing tower into the scrubbing tower—via a corresponding entrance—and further guided upwardly to a flue gas exit. Along this way through the scrubber tower the flue gas is brought into contact with the said liquid (fluid absorbent), often in a counter flow. Correspondingly the absorbent is introduced into the scrubber tower above the flue gas inlet, e.g. at the upper end of the scrubber tower, thus defining the section between the flue gas entrance and the absorbent inlet as the absorbing zone, which represents a contact area for said liquid and said flue gas.
It is further known to arrange nozzles at the upper end of the absorbing zone, by which the fluid absorbent is sprayed as fine particles (droplets) into the contact area to provide a preferably large reaction surface with the flue gas to be purified. The invention will be described hereinafter with respect to this generic design of a scrubber, but includes other designs as well, for example scrubber towers, where the gas is transported in a substantially horizontal flow direction.
The absorbent, also called scrubbing fluid, for example seawater, may absorb and/or chemically interact with various components/impurities of the flue gas, such as sulphur oxides and CO2.
A device and scrubbing tower as described above is known from EP 0756 890 B1.
It is further known from U.S. Pat. No. 5,246,471 to arrange one or more packings (trays) within the scrubber tower and across the flow path of the flue gas, upon which the liquid is sprayed. The trays have openings of defined size (cross section). By such a tray the liquid is temporarily stored onto the tray and thus a liquid bath formed. This allows the flue gas, penetrating the liquid bath upwardly, to get into a more intensive contact with the absorbing liquid. As a consequence, the degree of absorption is increased.
The invention starts from the object to further improve the degree of purification of the flue gas and/or to make the purification process more reliable.
The invention is based on the following findings:                I. The transfer area, which defines the reaction surface between gas and liquid in the contact area of a scrubber tower, depends—inter alia—from the gas volume (% by volume) within the liquid bath, the gas velocity within the contact zone, the (average) size of the gas bubbles and the vertical height of the liquid bath.        II. The degree of purification is dependent—inter alia—from the gas volume to be treated, the gas velocity, the size of the gas bubbles, the contact time between gas and liquid, the transfer area between gas and liquid.        III. Finer (smaller) gas bubbles increase the transfer area compared with larger bubbles (assuming both groups having the same total volume). The initial gas bubble diameter, i.e. the size of the gas bubbles when entering the liquid bath, again is dependent on the factors mentioned under II        
Modern power stations frequently vary their operating load, depending on the overall power demand, the type and quality of the energy source etc. This leads to considerable variations in the corresponding gas quantity, quality (gas composition) and gas velocity. In view of the parameters mentioned under I to III above the gas purification process often correlates with these parameters, i.e. the gas purification process is oversized or undersized. As a consequence the gas purification does not fulfil the corresponding economical and ecological demands any more.